1. Field of the Invention
The present invention relates to an object such as a riser and in particular to a three dimensionally fiber-reinforced riser and to the methods of making the same.
2. Description of the Related Art
It is a common product design goal to improve or replace conventional items with items having improved characteristics, such as improvements in strength, rigidity and durability, material qualities and economic concerns.
One industry where such enhancements are being made is in the archery industry. Archery risers, or simply risers, in the most basic form provide support for archery limbs. The risers can also support accessories such as but not limited to arrow rests, sight components, quivers, wrist straps, cable sliding bars, string stops and other accessories. The limbs bend symmetrically about opposite ends of the riser during the first of two stages of use, namely the draw stage, to store energy which, in turn, can be released during the second stage of use, namely the power stroke, to cause an arrow to be shot or projected from the bow. Stresses of varying magnitudes and orientations develop within the riser during use. Stresses can also develop within the riser during the manufacturing process.
One examples of a background patent is U.S. Pat. No. 7,258,113 to Pilpel et al. and titled Thermoplastic Composite Bow Riser, Limb and Cam illustrates a riser for an archery bow that is formed from a fibrous composite material, the matrix of which may be a high heat distortion thermoplastic polymer, a very high heat distortion thermoplastic polymer, or a combination thereof. The riser may incorporate a spine formed from a different polymer or composite than the rest of the riser, or from metal. A method for producing a riser for an archery bow includes the steps of introducing a polymeric composite into a mold from a first end of the mold to facilitate a particular orientation of components of the polymeric composite, molding the polymeric composite to produce a billet that approximates a net shape of the riser, and then machining the billet to the final shape of the riser. While the subject of this invention may work well for its intended purposes, its design and methods of manufacture can be improved upon.
Nothing is taught, shown or suggested in this patent as to how parts may be consolidated via a unitary molded composite component.
This patent requires the use of a spine made of a different material to achieve a desired structural integrity. The use of a spine can lead to delamination of the thermoplastic, as there exists mismatched physical and thermal properties between the spine and the remainder of the riser. The potential for delamination is enhanced due to the high stress conditions present during operation of the bow.
This patent also teaches the manufacture of a two dimensional product or laminate. One disadvantage of having a laminate flat part structure is that the fibers are only positioned in the two dimensions within the plane of the material, and ignores placement and orientation of fibers in the third geometrical dimension (i.e. in the direction of the thickness of the two dimensional laminate structure). In this regard, a two dimensional product of this type may only be useful in plane-stress state conditions.
This patent further teaches that the riser is machined to achieve the riser final shape and form. This requirement leads potentially to a host of deficiencies.
For example, the machined product may be subject to exposed fiber ends. Any fibers having exposed ends are subject to increased risks of pullout. The pullouts create voids in the product, and also can result in areas of decreased localized material strength. Crack propagation can also be a problem in areas of fiber pullout.
Still further, exposed fibers that remain intact can be subject to rapid oxidation and degradation, and there exists a possibility of separation between the fibers and resin.
It is particularly problematic that the locations which are most susceptible to these fiber problems are the areas where the material requirements are most demanding, namely, in the regions of the riser having three dimensional structures and where fine details or rapid changes in dimension are present. Examples of these regions include corners, generally curved surfaces and areas of radius.
Still further yet, the machined product can form relatively high friction surfaces, or even worse, be subject to varying degrees of friction along the surfaces. This situation is quite problematic for a product such as a bow riser, as arrows typically come into contact with the riser during launch and the changes in friction can alter the trajectory and/or speed of the arrow.
Thus, there exists a need for a three dimensionally fiber-reinforced composite riser and methods of making the same that solves these and other problems.